Corrosion Characteristics of Medical-Grade AISI Type 316L Stainless Steel Surface After Electropolishing in a Magnetic Field

Abstract

Stainless steel materials are widely used for multiple applica- tions because of their good mechanical properties and very good corrosion resistance in a number of environments. They are also used as biomaterials to manufacture conventional and novel medical devices. The stability of the surface oxide layer is one of the most important features of a biomaterial. Electrochemical polishing (EP) is the most extensively used surface technology for stainless steel. We have improved this surface technology by introducing a magnetic fi eld. With a new process called magnetoelectropolishing (MEP) we can im- prove metal surface properties by making the stainless steel more resistant to halides encountered in a variety of body fl uids, such as blood, saliva, urine, etc. Corrosion research results are presented on the behavior of the most commonly used material—medical-grade AISI Type 316L (UNS S31603) stainless steel—applied for human body implants, stents, and devices. Three basic environments have been adopted for the studies: pure distilled water, the Ringer's body fl uid, and 3% sodium chloride (NaCl) aqueous solution (the most aggressive environment). The study results cover open-circuit potential and polarization curve characteristics of austenitic stainless steels (Types 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), and 316L), and a ferritic stainless steel (Type 430 (UNS S43000)). The comparison of the corrosion behav- ior of the stainless steels' surface after two electropolishing processes carried out in the absence (EP) and presence of the magnetic fi eld (MEP) is reported. The experiments were car- ried out at room temperature (25°C). It has been found that the proposed MEP process shifts the corrosion potentials into the direction of greater corrosion resistance.